Wireless Smart Charging System for Mobile Devices Project Description Jacie Unpingco Western Washington University EE Class of 2015-2016 1
Introduction The proposed project is a wireless smart charging system. This device will charge the users mobile devices wirelessly and prevent overcharging. The user will connect a receiver to the charging port on the mobile device that can be left in the phone and place the phone on a mat to be charged. LEDs on the mat will be used to inform the user of the current charge on their phone. The charging mat will be small and portable so that it can be used anywhere. Product Electrical Specifications Power Requirements Charging Mat Max power output: 5 W Max output voltage: 5 V Receiver MCU Max power input: 5 W Max output voltage: 5 V Special Environment Requirements The charging pad will operate at a range that allows mobile device batteries to operate at without incurring battery damage. The charging pad will best operate at room temperature, 21 C. Lowest Maximum Operating Temperature = 10 C Highest Minimum Operating Temperature = 37 C General Requirements Will follow A4WP and PMA s wireless charging standard, Rezence, and follow FCC parts 18 and 15B. System Design Formulation and Specifications This project will be designed using the Freescale Kinetis KL0x entry-level, ultra lowpower MCU family, more specifically the FRDM-KL05Z-ND. This is the ideal microcontroller for this project because it will provide enough input/outputs for the LEDs and on/off switch required for the charging pad. This MCU is ideal for the highest possible efficiency of power transfer between the receiver and transmitter. 2
It also has a 48 MHz core frequency, which is more than fast enough for the specifications of this project. The MCU also has a memory interface of up to 32 KB program flash memory and 4 KB RAM. The receiver and the transmitter will each have their own MCU s however they will use the same type so the specifications will be the same for each PCB. 3
Software Requirements The software used to develop this project will use the Kinetis Design Studio with the implementation of C language. The MCU will encode bits to send a signal from the transmitter to the receiver. If the receiver gets this signal, a response is sent back and the transmitter is configured for power transfer to charge the mobile device. The MCU will also control the LEDs that indicate to the user the status of the charging pad and also control the charging of the actual mobile device. PCB Size Limits To be a small and portable device that is not a nuisance for users, the size requirements must be as minimal as possible. The PCB and its components must not exceed 5in. x 3.5in. x 1.5in. (LxWxH). This is also due to the charging mat needing to not be very thick. User Interface Requirements The user interface of this device will consist of a component the user will interact with and a component in which the user will view. The user will be able to toggle the charging pad between an on and off mode at their leisure on the side of the charging pad. The LEDs will be located on the top of charging pad will notify the user of two things: indicate to the user the amount of battery left on the charging pad and indicate if the pad is overheating by flashing. 4
Development Plan Prioritized List of Features 1. Heat resistant power mat 2. Automatically stop charging to prevent overcharging 3. Free positioning of mobile device on the charging mat 4. Automatic shut off if overheating occurs 5. LED charge indicators Features not part of this course 1. Flexible mat that can be used on any surface. Due to the time restraints and finding a material that will be able to meet the heat requirements, this is not a possibility for the prototype. 2. Sound will go off when the charge is full. This is just an additional feature that can be added on if I have enough time at the end of the quarter. 3. User defined set charging time for future designs. Schedule Date Task Winter Break Obtain mobile device to use for prototype testing, Android/Apple. Begin researching and designing initial schematics. 1/03 1/09 Begin designing transmitter and receiver schematics. 1/10 1/16 Continue designing initial schematics. 1/17 1/23 Continue designing schematics and order components. 1/24 1/30 Finalize schematics and layout boards. 1/31 2/06 Build/test transmitter board. 2/07 2/13 Build/test receiver board. 2/14 2/20 Resolve any issues and test again. 2/21 2/27 Finalize boards. 2/28 3/05 Hardware reviews. 3/06 3/12 Study for finals. 3/13 3/19 Finals Week. 3/20 3/26 Spring Break. 3/27 4/02 Set up MCU communications and connect to mobile devices 4/03 4/09 Write/test transmitter code. 4/10 4/16 Continue working on transmitter code. 4/17 4/23 Write/test receiver code. 5
4/24 4/30 Continue working on receiver code. 5/01 5/07 Continue working on code and try initial testing with mobile phones. 5/08 5/14 Continue working and testing the wireless charging system. 5/15 5/21 Prepare for code reviews and start on presentation visuals. 5/22 5/28 Code reviews. Conduct troubleshooting. 5/29 6/04 Test, debug, & finalize the wireless charging system 6/05 6/11 Prepare and present final project. Development of Hardware and Software The electronics and the charging pad prototype will be produced in the electrical engineering labs on campus using the necessary hardware and software development tools provided to students. I will be using the Freescale s Kinetis Design Studio program on the computers in the labs for my programming since it is a computer program that I have used many times in previous classes. While developing my prototype, I will also be using Multisim to simulate schematics that I have designed to check that they work as I expect them to before implementing them in real life. For the hardware, the charging pad will house the microcontroller and main circuitry for the wireless system. The charging pad will be made of a very thin durable plastic so that the receiver and transmitter can communicate. The bottom of the pad will have two adhesive strips so that the charging pad does not move while sitting on a table. I will also be using equipment provided in the labs like the power supplies, digital multi-meters, function generators, and oscilloscopes to test and debug my prototype throughout the Winter and Spring quarters. Safety Plan In the case that the charging pad overheats or the mobile device gets too warm, the LEDs on the charging mat should flash red. The user should then remove the mobile device from the charging pad and proceed to turn off the mat by switching the on/off switch on the pad. If the charging pad does not perform at full power, the unit should be plugged into the wall so that the charging pad can recharge. These precautions will prevent the user from personal injury and also avoid damage to the charging system. Description of Demonstration Prototype and Materials The prototype for my wireless charging system will be displayed on a table in one of the labs accompanied by a poster with a brief description of the product, schematics, and more. I will be supplying the mobile devices and their transmitters and the charging pad with the receiver inside that I have designed and produced. The 6
prototype can be used with the mobile devices I have supplied or the personal mobile devices of the people at the presentations if they so choose. Preliminary Parts List Part Price Lead Time FRDM-KL05Z-ND $15.00 2-3 weeks LEDs (x5) $0.53 5-10 days Resistors (x5) $0.10 5-10 days Capacitors (x3) $0.10 5-10 days Slider Switch $0.85 5-10 days 7